Enhanced micropropagation response and biocontrol effect of Azospirillum brasilense Sp245 on fruit-tree rootstocks

Abstract Free-living plant growth-promoting rhizobacteria (PGPR) can be used in a variety of ways when plant growth enhancements are required. The effects of the PGPR Azospirillum brasilense Sp245 have been assessed on micropropagation of three fruit tree rootstocks: Mr.S 2/5 (plum), GF 677 (peach x almond hybrid) and MM 106 (apple). Sp245 is a motile, free-living, gram-negative bacterium that occurs in the soil, capable of nitrogen fixation and phytohormones production. Tests with Mr.S 2/5 revealed that inoculated plantlets rooted in advance obtaining also a higher rooting percentage compared to the control. Positive results due to the presence of Sp245 have also been achieved during the acclimatation phase of Mr.S 2/5, GF 677 and MM 106 micropropagated plants. Interestingly, A. brasilense Sp245 revealed a biocontrol activity against Rhizoctonia solani and Phytophthora nicotianae detected in vivo and through in vitro inhibition tests. The biocontrol activity was confirmed by DGGE (Denaturing Gradient Gel Electrophoresis) profiles of microbial communities in the rhizosphere. Results acquired suggest that A. brasilense Sp245 can be convenientely used in substitution of chemicals during rooting and acclimatation phase of micropropagated plants. Finally, a bacterial formulation and a method for biofertilization and bioprotection of vegetal material with Sp245 have been developed.